Nottingham City Centre neighbourhood policing inspector Ruby Burrow said: "New legislation, enacted over a year ago, limits the supply of illegal psychoactive substances, resulting in a resurgence of street dealing and the use of the internet.

"One of the most common versions of these substances is 'mamba' or 'spice', a synthetic that mimics the effects of cannabis, but often in extreme ways.

"Those who use these substances, especially in a public environment, put themselves at significant risk of harm.

"We're working closely with partners and other organisations to curb supply, support vulnerable users, offer signposting to services that can provide help and support to users who wish to address any dependences they may have and encourage healthier lifestyle choices.

“Our focus, along with other agencies, is to keep people safe and encourage them to seek the help that's available.

"We do use legislation but only when it is absolutely necessary. However, action will always be taken against those supplying these substances.

“A high number of people are under investigation for and are likely to be prosecuted for the possession and supply of ‘mamba’ ‎but they have voluntarily complied with our investigations and, as such, have not needed to be arrested.

The number of arrests is so low because of this but it doesn't mean people aren't being interviewed and charged.

"I would encourage members of the public to provide information regarding the illegal supply of psychoactive substances by calling us on 101 or Crimestoppers, anonymously, on 0800 555 111.”

Nottinghamshire Police and Crime Commissioner Paddy Tipping said the Black Mamba and Spice problem on the city's streets is a priority.

He added: "These drugs are incredibly dangerous. People need to look after themselves and this just proves that point.

"It is a really difficult area for the force but it is being treated as a priority.